1. Field of the Invention
A digital signaling device for use with a digital transmission network comprising a signal generator means to generate a digital signal for transmission over the digital transmission network to a remote site and a signal recovery means to recover the transmitted digital signal received from the remote transmitting site.
2. Description of the Prior Art
Conventional to modem communications comprises transmission of analog signals over existing telephone lines or dedicated transmission lines. Generally, a carrier signal is also transmitted as a positive indication that the signal received is a valid signal to properly control the associated electronic data processing equipment. Commonly the EDP equipment generates a request-to-send signal which is fed to a modem to indicate that the EDP equipment is ready to transmit data. Similarly, a carrier detect signal is generated by the receiving modem which is fed to its associated EDP equipment to indicate that the modem is receiving carrier detect signals from the remote site to enable the EDP equipment. This system is satisfactory for an analog signal transmission system.
It is desirable to transmit data in its digital form rather than to convert the data to analog signals for transmission and then convert back to digital form at the receiving site. There are many advantages to the long range transmission of data in its digital form rather than in analog form. Long distance transmission of data consists of sending data between microwave stations which are on the order of thirty miles apart. Typically, analog data is subject to the cumulative building of errors over each link in the system. However, in a digital transmission system at each microwave site the digital signal is reconstructed to the customer's original data and then transmitted to the next microwave link. So, while in an analog system errors (noise, etc.) which develop in the customer signal are amplified and forwarded at each microwave link, in a digital transmission system the customer data is reconstructed, eliminating error at each microwave link. However, in a digital transmission system there are no analog control signals present. It is necessary to simulate the analog control signals such as the request-to-send/carrier detect functions to properly operate the correct software function of the existing EDP equipment.